As is known in the art, so-called “shadowing effects” generally refer to the lack of a direct line of sight between an incoming radio frequency (RF) signal and a receive RF antenna. The lack of a direct line of sight may result from an angle at which an incoming RF signal impinges upon an antenna element or an array of antenna elements. For example, if an array of antenna elements are disposed about the perimeter of a structure which is not transparent to RF energy, then RF energy incident on one side of the structure will be received by RF antennas on that side of the structure, but will be blocked from being received by RF antennas on an opposite side of the structure. Hence, the “blocked” RF antennas are said to be in the “shadow” caused by the blocking structure. Additionally, in some cases the antenna elements can create shadowing with respect to each other. Since signal degradation impacts the accuracy of any angle of arrival (AoA) computations, shadowing effects can be a major source of error in a missile seeker or other radar system.
To avoid such shadowing issues, in some systems, antennas have been placed in front of and separate from the blocking structure and in some cases even outside a radome structure. In systems which include both optical (e.g. infrared) and RF sensors, the RF sensor are sometimes physically located separate from and in front of the IR sensors and may also sometimes even be placed outside a radome structure. However, additional issues occur when antennas are placed proximate to or in front of optical sensors. For example, on a missile seeker, RF antenna structures may become heated (e.g., due to friction) and thus the RF antennas can become heat radiators. This results in interference with infrared (IR) sensors when the RF antennas are proximate the IR sensors.
Other attempts to avoid the signal degradation issues have positioned the antennas outside of and some distance away from the radome structure. However, such designs limit the number of antennas that can be used in the respective radar system. Additionally such design approaches may result in aerodynamic issues for radar systems disposed on a missile.